An image projection apparatus (projector) that projects an image on a screen (viewing surface) by using image data of a personal computer, data of a video image, image data stored in a memory card, etc. is known today.
The image projection apparatus (projector) projects light emitted from a light source device on the screen by using a micro mirror displaying element which is used as a micro mirror device, a liquid crystal plate, or the like, and forms an image on the screen.
A high-brightness discharging lamp is mainly used as a light source for the conventional light source device in the image projection apparatus. However, in recent years, a light source device that combines a solid light-emitting element emitting excitation light and a phosphor absorbing the excitation light and converting it into fluorescence of a wavelength in a predetermined wavelength band as a light source is being developed.
A semi-conductive element such as a light-emitting diode (LED), a laser diode (LD), an organic EL, or the like is used for the solid light-emitting element. The light source device using this kind of the solid light-emitting element has advantageous effects that can improve color reproductivity, light-emitting efficiency, use efficiency of light, and the like and achieve life prolongation, compared to the discharging lamp.
In addition, a design of an optical system can be easily achieved in the light source device using this kind of the solid light-emitting element, and the light source device has also advantageous effects that can achieve simplification of color composition, a low numerical aperture (low NA) of a projection lens (reduction of numerical aperture), etc.
However, when a laser light source is used for the light source device of the image projection apparatus, laser beam is coherent light having a regular wave front and has a high straightness. It is therefore preferable for the image projection apparatus to take a configuration in which laser does not directly enter person's eyes.
It is also preferable that laser beam of high energy strength does not hit a person's skin. Products having laser light sources are classified by the International Electrotechnical Commission (IEC60825) and the Japanese Industrial Standard (JIS C6802:2005), and the guidance that manufactures and users should be observed for each class is established. The guidance thereby contributes to the improvement in the safety of the products having the laser light sources.
In a light source device including the laser light source, in the image projection apparatus, a diffusion member relieving energy density of laser beam is provided in a traveling optical path of the laser beam such that laser beam with high output is not directly leaked to an exterior of the image projection apparatus to contribute to the improvement in the safety to the laser beam.
However, if the diffusion member deviates from the traveling optical path of the laser beam due to the falling etc. of the image projection apparatus, the laser beam is directly leaked to the exterior and therefore the safety to the laser beam is reduced. There is therefore proposed an image projection apparatus including a drive device that integrally rotates a fluorescent member and the diffusion member, and a light-shielding member engaged with the diffusion member, and configured to disengage the light-shielding member from the diffusion member when the diffusion member deviates from the traveling optical path of the laser beam, to move the light-shielding member at a position where the diffusion member exists by a centrifugal force, and to shield the laser beam, to prevent laser beam with high output from leaking to the exterior when the diffusion member deviates (see Paten Literature 1).
Moreover, Patent Literature 1 discloses a configuration including a detecting device detecting that the diffusion member deviates from the traveling optical path of the laser beam, or a detecting device detecting that the light-shielding member moves, and stopping the light emission from a laser light source.
However, anyway, the image projection apparatus disclosed in Patent Literature 1 presupposes that the diffusion member deviates from the traveling optical path of the laser beam and does not consider a case where a part of the diffusion member breaks even if the diffusion member does not deviate from the traveling optical path of the laser beam such that the diffusion member does not exist in the traveling optical path of the laser beam in a normal state. A further improvement is required in planning the safety to the laser beam.